Titan Quest for 4 dollars is just RIDICULOUS value. It's no Diablo 2, but it's a LOT of fun the first few times through, and you can make an absolute SHITLOAD of capable character combination, most of them actually fun to play too.

Seriously, if you don't have it, eat a sandwich less next week and get it. That's just a stupidly good deal.

Edit : As for the no-expansion, you won't miss it. The expansion has a few good areas, but also a few just TERMINALLY boring ones, plus the expansion's rubber-banding issue just killed the entire game for a ton of people.